The objective of the proposed research is to carry out mutagenicity testing with selected compounds of practical importance to humans. These include the food additive, saccharin, the anti-schistosomal drug, niridazole, two phenothiazine tranquilizers (triflupromazine and thioridazine), and the anti-epileptic agent, diphenylhydantoin. Two principal assay systems, the mouse and Drosophila melanogaster, as well as in vitro microsomal activating system, will be employed in co-ordinated experiments. In the mouse, procedures to be followed include the dominant lethal test, the host-mediated assay, and in vivo cytogenetics (including the micronuclei test); in Drosophila, genetic procedures will be employed testing the recessive lethals, translocations, chromosome loss and nondisjunction. Drosophila will be used to assay compounds directly and used as an indicator organism to screen for mutagenic activity in body fluids of treated mice. Utilization of this battery of test systems is expected not only to provide extensive information on the mutagenic potential of these compounds, but to contribute as well to a far more comprehensive evaluation and characterization of mutagenic substances than is achieved in most testing programs.